Behavioral Determinants of Disease Transmission by Mosquitoes

Abstract

Mosquito-borne illnesses have shaped human history and continue to impose significant global public health burdens, with particularly devastating effects in socioeconomically disadvantaged areas. Blood feeding is essential for mosquito reproduction, as blood provides nutrients for egg development, and vector species are strongly driven to find and bite humans for this blood meal. These maternally-driven behaviors not only expose humans to pathogens but also promote mosquito population growth. Recent advances have deepened our understanding of the sensory systems and internal state regulation behind host seeking and biting. Here, we examine the behavioral and neurobiological mechanisms underlying mosquito-human interactions and their role in pathogen transmission and disease. We also highlight how these insights can inform emerging behavioral control strategies.

Introduction

Few aspects of entomology have shaped human history as profoundly as the blood-feeding behavior of female mosquitoes [1,2]. A blood meal initiates the female reproductive cycle by providing essential nutrients and chemical signals for egg development. Several days later, the female lays eggs and begins seeking a new host, repeating the cycle of blood feeding and reproduction and increasing her contact with humans over time. During blood feeding, mosquitoes can acquire and transmit blood-borne pathogens. Roughly half of the world’s population lives in areas at risk of mosquito-borne diseases. Although thousands of mosquito species exist, only a small subset is responsible for the majority of mosquito-borne illnesses and their devastating effects on human health. Major vectors of human pathogens include Anopheles mosquitoes, which transmit malaria parasites, and Aedes mosquitoes, which spread arboviruses such as Zika, dengue, and chikungunya [3]. Two species in particular, the yellow fever mosquito Aedes aegypti and the African malaria mosquito Anopheles gambiae serve as key models for this review: both show a strong, odor-guided preference for human hosts, and both are among the most heavily studied mosquito species, providing mechanistic understanding of their host-seeking and reproductive behaviors. These species that specialize in biting humans show physiological and sensory adaptations that make them particularly effective at targeting human hosts, underlying their roles in pathogen transmission and public health threats [4–6]. Here, we review the neurobiology of disease-vector mosquitoes, focusing on how the female’s reproductive drive shapes her behavior and enables pathogen spread and population growth. We also highlight recent advances in understanding these behaviors and discuss how these insights can inform optimized mosquito control strategies.

Blood as a maternal need

Ingesting blood, or hematophagy, is a feeding strategy found across diverse organisms, including mosquitoes, ticks, leeches, and bats [7]. Much of our foundational understanding of hematophagy traces back to Sir Vincent Wigglesworth’s pioneering work on the kissing bug, Rhodnius prolixus, in which he showed that, in addition to providing nutrients, blood feeding also triggers hormonal cascades that govern molting and reproduction [8]. His work established blood feeding as a behavioral and physiological trigger, a framework that continues to shape how we study hematophagous insects today. While obligate hematophagous animals, like the kissing bug, rely exclusively on blood for development and survival, mosquitoes are not obligate blood feeders, and only adult females consume blood meals. Both males and females feed on floral nectar to meet their metabolic needs, but females require blood as a source of protein and essential nutrients for egg development [9,10]. Given the central role of blood in reproduction, female mosquitoes have evolved sexually dimorphic sensory and feeding structures specialized for detecting, sorting, and consuming blood [11,12]. The female stylet is adapted to detect blood-specific tastants, like ATP and sodium chloride, directing ingested blood to the midgut for digestion rather than to the crop used for nectar storage [12–15]. These sensory cues promote successful engorgement, during which a female mosquito can double her body weight in a matter of minutes. This blood meal triggers a cascade of physiological and behavioral changes that support egg development [9,16]. In the days following feeding, blood nutrients are processed and directed for yolk protein synthesis and ovarian maturation. Coordinating the synthesis and allocation of these nutrients requires the integration of physical and chemical cues, with crosstalk between the gut, fat body, and nervous system [17–20]. Female Aedes and Anopheles mosquitoes are primarily monandrous: a single mating event enforces paternity and supplies enough sperm to last a lifetime, leaving blood feeding as the pace-setter for reproduction. A single blood meal typically yields approximately 100 eggs, though this figure varies considerably by species and blood meal source. Repeated cycles of blood feeding not only sustain mosquito population growth but also increase opportunities for the transmission of blood-borne pathogens (Figure 1). As a reproductive necessity, the maternal drive for blood shapes mosquito behavior and biting strategies, underlying their impact on human health.

Figure 1.

Blood is a reproductive need and a driver of mosquito population growth.

Biting strategies and human specialization

Among blood-feeding insects, Aedes and Anopheles mosquitoes show a remarkable degree of specialization in locating and biting humans. Recent work has identified sensory strategies and neurobiological mechanisms that directly underlie their effectiveness in targeting humans (Figure 2A). Although human-preferring species pose major public health threats, incidental biting by other mosquitoes can also contribute to pathogen transmission: Culex mosquitoes that primarily bite avian hosts can spread West Nile virus from birds to humans [21–23]. Mosquito attraction to humans relies on the integration of multiple sensory cues. Some cues, like visual contrast and carbon dioxide (CO₂), are broadly shared across vertebrate hosts, whereas others, especially odor profiles, are more host specific and contribute to preference. In addition, host-derived sensory cues vary in the spatial ranges over which they exert their effects according to their physical and chemical properties [24]. CO₂, a long-range cue, activates mosquito flight and primes subsequent sensory integration with body heat and skin odorants [25,26]. Gustatory receptors families like Gr1, Gr2, and Gr3 in Aedes aegypti and their orthologs AgGr22, AgGr23, and AgGr24 in Anopheles gambiae are expressed in the maxillary palps, and serve as potential CO₂ sensors [21–23]. Genetic knockout studies in Aedes aegypti demonstrated that CO₂ detection relies on Gr3 [27], and optogenetic activation of Gr3 neurons elicits a persistent predatory state [28]. While visual contrast alone does not specifically drive biting [29], it plays a strong role in promoting host-seeking when coupled with behavioral activation from CO₂ [30].

Figure 2.

Sensory and modulatory processes of mosquito host seeking and biting. (A) Sensory targets and their corresponding host cue modality during host seeking. (B) Circadian modulation of biting drive. (C) Reproductive modulation of biting drive.

Traditionally considered a close-range host cue, infrared (IR) radiation from body heat has recently been identified as a mid-range cue that attracts mosquitoes from up to 0.8 m. Thermal IR sensing involves temperature sensitive channels, including TrpA1, as well as opsins (op1, op2) expressed in the antennal tip [31]. Humidity gradients serve dual roles: they guide females to oviposition sites as well as serving as a short-range host cue, as human skin generates a locally elevated humidity gradient. Humidity sensing requires the ionotropic receptor Ir93a in the mosquito antenna, and disruption of this receptor impairs blood feeding in both Anopheles gambiae and Aedes aegypti [32]. Further functional analysis in Aedes aegypti reveals distinct groups of Ir40a-dependent Dry Cells and Ir68a-depedent Moist Cells within the mosquito antenna that respond to dry or humid air respectively [33]. Unlike olfactory or other physical cues, contact-dependent gustatory mechanisms contribute to host evaluation and ultimately determine whether biting occurs. In Aedes albopictus, tastants from human skin and sweat promote biting. These cues are detected by the labellum, a taste organ that contains organized sensilla with distinct electrophysiological responses and is enriched for chemoreceptor families including gustatory receptors (Grs), ionotropic receptors (Irs), pickpocket channels (ppks), and TRP channels (Trps) like painless1 [13,34].

Although host-seeking relies on multimodal cues, olfaction plays a critical role in human specialization (Figure 2A). In Aedes aegypti, disruption of the odorant receptor co-receptor Orco abolishes preference for human odor, demonstrating its necessity for host discrimination [35]. Similar defects in odorant discrimination are reported in Anopheles gambiae with Orco-defective neurons and Anopheles coluzzi Orco mutants, although effects on host species preference remain to be tested [36,37]. In Aedes aegypti, the evolution of human preference is linked to increased expression of a specific odorant receptor Or4 that is activated by compounds present in human odor [6]. At the neuronal level, human and non-human odors are differentially represented in the antennal lobe, showing species-specific patterns of glomerular activation [38]. Notably, mosquito olfactory neurons can co-express multiple ligand-specific chemosensory receptors, including members of both the Or and Ir families, deviating from the conventional one receptor per neuron model, suggesting redundancy in odor coding that may support robust host recognition in a complex odorant landscape [39–41]. Electrophysiological studies of second-order olfactory neurons support combinatorial coding and interglomerular interactions that may influence olfactory processing and host-seeking behavior [42]. Beyond overall human odor preference, mosquito attraction levels vary among skin-derived odor blends from different individuals, as demonstrated in both laboratory and semi-field studies in Aedes aegypti and Anopheles gambiae [43–45]. These findings highlight olfactory specialization as a key driver of human biting and a potential target for interventions aimed at reducing biting efficiency. Although olfaction is central to biting preference, human specialization is also shaped by ecological and evolutionary pressures. In Aedes aegypti, the shift towards human biting is thought to have been driven initially by climate and reliance on human-stored water for breeding, with urbanization emerging as a dominant factor in recent decades [46]. Areas of ongoing study focus on integrating functional analyses of olfactory coding with emerging connectomic maps of the mosquito brain to understand how host-derived cues are transformed into behavioral outputs [47]. Efforts are increasingly aimed at linking receptor-level activity and glomerular representations to defined downstream circuits that encode and prioritize human-specific odor signals. These approaches could reveal key circuit nodes and organizational principles that could be targeted to disrupt host seeking and biting.

Modulation of host-seeking drive

Although mosquitoes use robust sensory strategies to find humans, host seeking is not constant. Instead, it is strongly gated by the internal state of the female [48]. Reproductive status and circadian timing modulate biting drive, with near complete suppression at specific times of day or at distinct points in the reproductive cycle (Figure 2B and C). In the days following a blood meal, during egg maturation, female mosquitoes drastically reduce activity and biting drive, a behavioral state referred to as host-seeking suppression (Figure 2B). This has been most extensively characterized in Aedes aegypti where suppression occurs in sequential phases. Initial inhibition is likely mediated by mechanosensory feedback from the distended midgut after engorgement [49], followed by nutrient-derived signaling that activates satiety-related neuropeptide pathways in the gut, and finally by signals from the presence of mature oocytes that suppress host-seeking [16,50]. Importantly, these pathways can be independently manipulated; Neuropeptide Y-like Receptor 7 (NPYLR7) regulates host-seeking in Aedes aegypti and can be pharmacologically agonized to suppress biting even without protein consumption or egg development [51]. Host-seeking suppression occurs across Aedes, Anopheles, and Culex, though variation in its onset and duration points to species-specific regulatory mechanisms [52]. There is evidence that suppression involves modulation of peripheral sensitivity to host cues, such as lactic acid [53], and recent studies have identified signals outside of the brain that are key regulators of host-seeking [19,54]. How multi-organ communication aligns physiological state, sensory processing, and behavior remain important areas for ongoing investigation.

Daily biting rhythms are also well-documented, particularly in regions with high disease burden. Aedes mosquitoes are generally diurnal, while Anopheles mosquitoes tend to show nocturnal biting patterns (Figure 2C). Laboratory research has shown that light cues promote activity and biting in diurnal mosquitoes but suppress these behaviors in nocturnal species [55,56]. Recent work has also revealed interactions between circadian timing and behavioral persistence to the host cue CO₂, with peak biting times characterized by more sustained responses to CO₂ pulses in Aedes aegypti [57]. At the molecular level, circadian rhythms are regulated by conserved transcription-translation feedback loops (TTFL) and disruptions of core clock genes significantly alters activity patterns and behaviors across mosquito species [58–61]. Consistent with this, daily oscillations in olfactory sensitivity have been reported in both Aedes and Anopheles mosquitoes [62,63]. The circadian neuropeptide Pigment-Dispersing Factor (PDF) coordinates clock gene transcript oscillation across circadian neuron clusters in the brain and controls daily behavioral timing, and loss of PDF leads to significant reduction of morning activity levels and biting efficiency in Aedes aegypti mosquitoes [57]. Circadian clocks can also directly influence pathogen transmission. In Anopheles gambiae, many genes in the salivary glands that are essential for efficient blood feeding are under circadian control, promoting nocturnal feeding [64]. Malaria parasites also exhibit intrinsic rhythms and modulate transmission efficiency, suggesting that vector and pathogen clocks interact to affect transmission dynamics [64,65]. Ongoing work aims to establish mechanistic links between core clock function and the host-seeking modulation, and to determine how parasite, vector and host clocks jointly influence infection outcome revealing how co-evolved timekeeping systems shape the transmission of vector-borne disease.

Reproductive behaviors

One key driver of the increasing risk of mosquito-borne illnesses is the growth in mosquito populations and their expansion into new territories, which is fueled by highly efficient and adaptive reproductive behaviors. As a female becomes gravid and prepares to lay eggs, she undergoes behavioral reprogramming and sensory retuning to facilitate successful oviposition. Egg laying on suitable substrates is critical for reproductive success, as offspring survival depends entirely on the characteristics of the oviposition site. These include appropriate hatching cues, absence of toxins/salt, sufficient nutrients for larval development, protection from predators, and optimal population density. Female mosquitoes typically lay their eggs in stagnant water, making humidity-seeking behavior critical for identifying appropriate oviposition sites [66]. Beyond its role in sensing host skin humidity, the ionotropic receptor Ir93a is also required for gravid females to locate egg-laying sites in both Anopheles gambiae and Aedes aegypti [32]. Additionally, gravid females are attracted to volatile odor cues from potential egg-laying sites. Often, these chemical cues indicate the presence of nutritional sources, including the microbial volatile geosmin [67]. Recent work has also identified a clock-gene-dependent state of hyperactivity that aids in egg-laying site search [68]. Once she has landed on a potential substrate, the gravid female further evaluates suitability by assessing water salinity using her forelegs, which is dependent on the DEG/ENaC channel ppk301 [69]. Additional studies have shown that communal olfactory cues from other gravid females influence egg-laying decisions that help regulate population density, mediated via Orco and the CO₂ receptor Gr3 [70].

While cyclical blood feeding and egg laying sustain mosquito populations in tropical and subtropical climates throughout the year, species in temperate regions often rely on alternative reproductive programs to cope with seasonal variation. Many enter diapause, a hormonally-regulated state of developmental arrest that enables survival through unfavorable environmental conditions [71]. Aedes albopictus undergoes maternally-instigated embryonic diapause and produces developmentally-arrested and hatch-resistant eggs that survive harsh winters and hatch when favorable conditions return in the spring [72,73]. Day length and temperature serve as common cues for diapause induction across species with differing overwintering strategies. In Culex pipiens, which diapause as adult females, disruption of the circadian clock triggers inappropriate diapause under summer-like conditions [74]. Although they do not diapause, Anopheles mosquitoes also show seasonal changes and can enter aestivation, a period of dormancy to survive hot dry seasons [75,76]. Future work will investigate how circadian clocks, seasonal cues, and reproductive state are integrated at the molecular and circuit level to coordinate mosquito behavior and population dynamics and whether these mechanisms are conserved or divergent across species with differing seasonal reproductive strategies.

Behavioral targets for mosquito control

The threat from mosquito-borne illnesses in the early 20^th century promoted research into insect physiology and the development of coordinated mosquito control strategies that led to disease prevention in war time and, later, in peace [1]. Traditional efforts have largely relied on insecticides like DDT that target adult mosquito populations and early developmental stages. Although new synthetic insecticides aim to improve safety for human health, they continue to raise ecological concerns related to unintended effects on non-target insect species important for agriculture and ecological conservation. Additionally, widespread insecticide use imposes strong selective pressure, which leads to the rapid emergence of resistance [77]. Despite their historical success, these limitations highlight the need for alternative control strategies. One approach that has been successfully applied across multiple species is Sterile Insect Technique (SIT), which targets mating by using sterile males to mate with females [78–80]. Because females typically mate only once, those that mate with radiation-sterilized males will neither produce viable offspring nor remate with a fertile male. Although SIT has achieved substantial success in insects such as New World screwworm flies, Mediterranean fruit flies, and tsetse flies, its application to mosquitoes has proven more challenging because of complex population dynamics, difficulties in achieving sufficient sterile-to-wild male ratios, and the fitness costs associated with irradiation. An alternative approach is the release of Wolbachia-infected mosquitoes. Depending on the Wolbachia strain and mosquito system, Wolbachia can induce cytoplasmic incompatibility, which reduces the viability of embryos produced from incompatible matings, and can also reduce mosquito competence for certain pathogens [81]. These effects provide a means of suppressing mosquito populations or reducing pathogen transmission without requiring the release of genetically modified mosquitoes. However, the long-term effect of Wolbachia-mosquito and Wolbachia-pathogen interactions require continued evaluation. Targeted transgenic approaches, like gene drive (GD) and the release of insects carrying a dominant lethal gene (RIDL) also target mosquito reproduction either by inducing offspring lethality or reducing pathogen transmission [81]. However, there are still major ethical and regulatory issues that these transgenic methods need to navigate, and the ecological and evolutionary consequences of these approaches require careful evaluation to minimize unintended impacts [82].

Emerging mosquito control strategies increasingly exploit the neurobiology of pathogen-spreading behaviors. Insights into mosquito sensory preferences and their neural basis have refined “lure and kill” strategies. Extensive work to understand chemical cues and chemosensory detection has identified key attractants involved in host seeking and oviposition, enabling the development of more effective and commercially viable traps. For example, beetroot peel extract has been shown to be a low-cost alternative to the oviposition site attractant geosmin with promising applications in developing countries [67]. Other sensory-based strategies include acoustic traps that target wingbeat frequency preference and visual markers that mimic swarming sites, signals usually detected by males searching for potential mates [83,84]. Advances in understanding the internal regulation of mosquito behavior offer additional targets for intervention. Identifying receptors that modulate host seeking or mating could enable structure-guided drug design of small molecule antagonists/agonists that reduce biting rates or reproductive success [85]. These approaches illustrate how mechanistic insights into mosquito neurobiology are opening new avenues for vector control beyond conventional insecticides.

Concluding remarks

In Insects and the Life of Man: Collected Essays on Pure Science and Applied Biology, Wigglesworth argues that solving insect-borne disease requires understanding insect physiology on its own terms and that effective control follows from mechanism, not the other way around [1]. Mosquito behavior and physiology are inseparable from human health, and blood feeding is essential for female mosquito reproduction, making biting a persistent threat. Despite scientific progress, mosquito-borne diseases remain widespread, with key species continuing to expand in number and range. Studying the neurobiological control of mosquito behaviors serves both basic science as well as vector control by illuminating principles of sensory coding and behavioral regulation while identifying new targets and refining existing strategies. Mechanistic insights into how mosquitoes detect and select human hosts are enabling next-generation traps and lures that exploit these sensory cues. Because mosquitoes rely on multiple, partially redundant sensory pathways (olfactory, thermal, visual, etc.), attraction can be hijacked at several independent points, giving control programs flexibility to choose strategies suited to local environmental, regulatory, and financial constraints. Deorphanized olfactory and gustatory receptors offer a starting point for structure-based design of synthetic agonists and antagonists, which could yield improved lure-and- kill attractants or longer-lasting repellents than current compounds like DEET. Push-pull strategies, which combine attractive lures with spatial repellents, could similarly be refined as specific receptor-ligand pairs are identified, allowing formulations to be tuned to the receptor repertoires of locally dominant vector species. Insights into reproductive physiology, including the molecular pathways triggered by mating and blood feeding, could enable interventions that directly suppress egg production or fertility, complementing existing approaches such as sterile insect technique and Wolbachia-based population suppression. Because biting, mating, and host seeking are all gated by circadian and reproductive states, tools that shift or suppress these internal rhythms could reduce human contact without relying on insecticides, and could also sharpen the timing of existing interventions, for example, coordinating indoor spraying or bed net use with a vector’s peak host-seeking window. The field has also generated major methodological advances, particularly in genomic and genetic tools, enabling key discoveries in the past decade. New resources, such as the mosquito cell atlas and emerging connectomic tools, are poised to accelerate identification of neural circuits underlying behavioral regulation [47,86]. Translating these discoveries into pharmacological, genetic, or other interventions will be essential for a robust and multifaceted mosquito control arsenal.

HIGHLIGHTS:

• Blood feeding drives mosquito reproduction and human contact

• Blood feeding and its human specialization underlie risk of pathogen transmission

• Multi-modal sensory systems underlie human-specialized host seeking

• Reproductive state and circadian clocks gate mosquito biting drive

• Neurobiological insights inform emerging behavioral control strategies